The Pentagon is now admitting that air strikes against ISIS will ultimately prove ineffective in slowing its advance, and NBC is reporting that any military effort to stop ISIS in Iraq is a 10- to 20-year proposition. Not gonna happen. Secretary of Defense Chuck Hagel has called ISIS an imminent menace to the United States, which ISIS has confirmed by issuing direct threats against the United States. “We will raise the flag of Allah in the White House,” and “If the United States bomb Iraq (N.B.: which Obama has done), every American citizen is a legitimate target.”

So if air strikes aren’t the answer, and we are not ready - and assuredly we are not - for another ground war in the land of Saddam, what is our alternative? Once again, the Constitution provides the solution, in a little noticed provision in Article I, Section 8. Among the enumerated powers we the people delegated to Congress is the following: “To declare war, grant letters of marque and reprisal, and make rules concerning captures on land and water.” (emphasis mine).

The fact that this delegated power of action occurs in the same sentence that authorizes Congress to declare war indicates that it deals with the authority of Congress to issue directives regarding the use of force to protect the security of the American people from foreign threats. What is a “letter of marque and reprisal?” “Marque” refers to a boundary, and “reprisal” to the redress of a wrong. As Wikipedia correctly puts it, “A ‘letter of marque and reprisal’ would involve permission to cross an international border to effect a reprisal (take some action against an attack or injury) authorized by an issuing jurisdiction to conduct reprisal operations outside its borders.”

While originally it was designed to deal with marauding pirates on the open seas, the power of action described here clearly refers to a situation in which there is a threat to the United States and its people but there is no sovereign state against which to declare war. It’s designed to deal with rogue agents who represent a danger to our safety. In other words, it’s for renegades just like the head of ISIS. So the way forward is for Congress to issue a letter of marque and reprisal naming Abu Bakr al-Baghdadi, the self-declared caliph of his new Islamic fiefdom, as the target.

For this action to be constitutional, the decision must be made by Congress, not the president, after full and open debate before the nation and the world. Congress would then issue the letter of marque and the commander-in-chief would execute it. We would then mobilize the resources of the intelligence community and the military to locate him and take him out, whether with a drone, a missile strike, or Seal Team 6. And we would let his jihadi comrades know that everybody who is anywhere near him when we find him is at mortal risk. If they choose to hang around, their blood will be on their own heads.

It’s time to cut off the head off the snake. And if al-Baghdadi is replaced by someone just like him, we cut the head of that snake off too. Lethal force is the only language the armies of Allah understand, and it’s time to send them a message. Before they send us one.